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Metastatic triple negative breast cancer with NTRK gene fusion on tissue but not on ctDNA molecular profile
  1. Nupur Singh1,
  2. Rishika Singh1,
  3. Brennan Decker2,
  4. David Robins2 and
  5. Gregory Vidal1,2
  1. 1College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee, USA
  2. 2West Cancer Center and Research Institute, Memphis, TN, USA
  1. Correspondence to Nupur Singh; nsingh8{at}


A woman presented to medical oncology with almost 4 years of untreated, slowly progressing, triple negative metastatic breast cancer to the lung. About 15 years prior, she was diagnosed with invasive ductal carcinoma of the right breast with ipsilateral chest wall recurrence 6 years later. Comprehensive molecular profiling of a metastatic lesion detected a hotspot ETV6-NTRK3 fusion, which was not present on circulating tumour DNA or molecular profile performed 4 years prior. A second look pathological examination demonstrated tumour characteristics consistent with secretory breast carcinoma. Identification of ETV6­-NKRT3 fusion allowed for treatment with larotrectinib, a tyrosine kinase inhibitor specifically indicated for secretory breast carcinoma. After 3 months, she experienced a partial response.

  • Breast cancer
  • Screening (oncology)
  • Drugs and medicines

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  • Contributors All authors contributed to the writing of this paper including NS, RS, BD, DR and GV. We would like to thank Dr Gregory Vidal for introducing us to this patient’s case.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Case reports provide a valuable learning resource for the scientific community and can indicate areas of interest for future research. They should not be used in isolation to guide treatment choices or public health policy.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.